1. Field of the Invention
The present invention relates to the removal of debris from oil and gas wells. More particularly, the present invention relates to an improved method and apparatus for removing debris from an oil and gas well tubular or tube shaped member or pipe (e.g., casing) wherein the apparatus employs specially configured petals and slots that enable flow outside the tool body in both up and down directions.
2. General Background of the Invention
In general, the removal of debris from oil and gas wells is well documented. There are many examples of prior art which include scrapers and brushes to mechanically clean the interior surface of casing of the well. Likewise, there are examples of tools designed to remove the debris from the wellbore after it has been scraped and/or brushed. This is an important function of a wellbore cleanup operation as the removal of junk and debris help mitigate against failure of downhole equipment, particularly when circulation of wellbore fluid alone is insufficient to ensure hole cleaning. Magnets are often used for this purpose, however not all wellbore debris is ferrous. Therefore, some debris must be removed by a mechanical means.
Some prior art devices (e.g., see U.S. Pat. No. 6,250,387) use a wiper cup made of a flexible but high strength rubber, typically supported by metal wires which are moulded into the rubber. The rubber and wire work together to provide sealing and wiping capability as well as resistance to tearing. One problem with this type of device is that the wiper cup is adapted from use as a one directional seal whereby fluid pressure on the inside of the cup bellows the cup outwards to create a seal.
Fluid pressure on the outside of the cup causes it to partially collapse, allowing pressure to bypass the cup. The wiper cup can hold pressure in only one direction. It cannot allow significant volumes of fluid or debris laden fluid to flow past it in the opposite direction, particularly the volumes required to perform an effective wellbore cleanup. This is due to the shape of the cup which form a continuous seal on the inside of the wellbore, as well as the materials used which while being rubberized are still relatively stiff and resilient in order to be robust enough to work in a downhole environment.
In order to allow the high volume of debris laden fluid to pass the tool, the device of U.S. Pat. No. 6,250,387 discloses a series of check valves. This allows fluid to pass through the tool in one direction bypassing the filter, and works in conjunction with the wiper cup to divert fluid through the screen in another direction. The check valves which act as a diversion means for the filtered fluid often become blocked by larger debris and junk resulting in the wellbore fluid partially or completely bypassing the filter and therefore rendering the tool useless. The wire wrapped screen used on this device is prone to damage whereby junk becomes trapped in the annular volume between the screen and the casing. Due to rotation of the tool, the wire screen can become damaged and fail catastrophically.
The largest external components are used for stand-off and are attached such that they rotate with the tool. It is commonly accepted that wellbore cleanup tools which feature non-rotating centralizers (centralizers which can remain stationary while the tool rotates) prevent casing and tool wear. The ‘burst disks’ used on the U.S. Pat. No. 6,250,387 as an emergency bypass are prone to opening accidentally which allows partial or complete bypass of the filter, which occurs most often when the drilling rig ‘pumps a slug’ (a method of lowering the fluid level in the wellbore by placing an artificially high density pill into the work-string which over-pressures the burst disk).